Iwas woudnering if you could help me with this problem. The answer key says that the answer is D and I have no idea why. The chart, included in the link, reads off a value of about .5 for the G locus for the year 1980

Question

Finding the percent heterozygous should be as sipmle as 2(.5)(.5)=.5 I got .5 for g by simply taking the complement of the dominant trait G, gray, by doing 1-.5

Clearly I am doing something wrong. I do not know what I am doing wrong. Iw as woudnering if you could tell me the secret to this question as I can not get .67 for the life of me

Only 28% of the people who took this test got this question right and I can't figuer it out either...

h t t p : / / i m g 5 2 6 . i m a g e s h a c k . u s / i m g 5 2 6 / 4 6 7 7 / b i o f . p n g

Assuming that the population was in
Hardy-Weinberg equilibrium for the G locus, what percentage of the gray moths that emerged in 1980 was heterozygous?
(A) 0%
(B) 25%
(C) 33%
(D) 67%
(E) 100%

Answer 1

Sorry, my original field was physics and my graduate degrees are in in engineering. Any high school student has more background in biology than I have.

Answer 2

What you did was all right, but they're not asking a normal question involving all of the moths. They're asking for the percentage out of only the grey moths, which eliminates the moths with the gg phenotype.

Another, more useful way of finding the percent of heterozygous moths is using the formula

2pq = 1 - p^2 - q^2

*p is the frequency of the dominant gene, so p^2 is the % of the homozygous dominant moths (GG)

*q is the frequency of the recessive gene, so q^2 is the % of the homozygous recessive moths (gg)

As you said, p and q were both 0.5, so when they are squared, they both turn out to be 0.25. When we put them into the formula, we get

2pq = 1 - 0.25 - 0.25
= o.5

which is what you got as your answer.

However, since the question asks us for the percentage out of only the grey moths, we do not include the gg phenotypes as part of the final calculation. What's left is 75% of the population, of which 2/3 are heterozygous. That, converted into decimal form is 0.67, or 67%.

Answer 3

Borrowing from some of the work detailed above:
Solution: They're asking for the percentage out of only the grey moths, which eliminates the number of moths with the gg phenotype.
Grey (GG) moths = 0.25(2000) = 500
Grey (Gg) moths = 0.5 (2000) = 1000
The question asks us for the percentage out of only the grey moths: Therefore, 1000 (Gg) / 1500 (GG + Gg) is 0.67, or 67%.